The major objective of this is to develop a model of a needs (nature) and prevalence (extent) assessment for the Mexican-origin population that will be relevant for planning prevention interventions in an urban (San Antonio) and U.S. Mexico border community (Laredo, Texas). Intravenous use of heroin and other illicit substances by Mexican Americans in these areas, as in other areas of the country with high concentrations of Mexican-origin persons, is at a disproportionately high level. The proximity of Mexico, a major source of heroin and cocaine into the United States, facilitates access to these drugs by residents in these communities. Drug assessment and prevalence studies among these groups is further complicated by the presence of the international border which set jurisdictional authority, constrains public health efforts, and complicates data collection. Recent events involving escalation of drug- related corruption and violence along the border forewarn of an increased availability of intravenous drugs in the communities and therefore increased risk for spreading Human Immunodeficiency Virus (HIV). The relationship between IVDU and HIV has created a demand for more accurate techniques and methods in estimating IVDUs among the population as a whole, and in particular among Mexican-origin and Latino populations. This study argues that current techniques and methods in estimating IVDUs among the population is limited. The specific aims of this study are to: conduct a drug epidemiology and needs assessment study of the adult intravenous drug using population in two areas of South Texas - San Antonio and Laredo; develop a model intravenous drug use assessment approach that meets particular social and cultural characteristics and conditions of the Mexican-origin populations in the Southwest; implement and test the validity of this model over a three year period; and enhance UTSA's capabilities in the development and implementation of substance abuse research among Latino faculty and students. This model would then be applicable to Southwestern urban and border communities.